Photolithography is a process to pattern parts of a thin film or the bulk of a substrate. Photolithography uses light to transfer a pattern from a photomask, i.e. a reticle, to a light-sensitive layer, i.e. a photoresist, on the substrate. The light-sensitive layer is exposed to a pattern of light by transmitting light through the photomask onto the light-sensitive layer. The exposure to light causes a change that allows parts of the light-sensitive layer to be removed by a developer, and thus the pattern from the photomask is transferred to the light-sensitive layer.